Terminal



J. KELLEHER June 17, 1930.

TERMINAL Filed Feb. 29, 1928 INVENTOR. Ja/rzes ffellelzer Patented June 17, 1930 UNITED STATES PATENT OFFICE I JAMES KELLEHER, OI CHIPPA'WA, ONTARIO, CANADA, ASSIGNOR TO HARPER ELEC- TBIC FURNACE CORPORATION, OF PHILADELPHIA, PENNSYLVANIA, A CORPORA- TION OF NEW YORK TERMINAL Application filed February 29, 1928.

This invention relates to terminals for electric furnaces and more particularly to resistor terminals for resistors of the zigzag type.

In electric furnaces there is a temperature gradient more or less steep from the point where the lead wires connect to the terminals to the high temperature portion of the circuit, namely, the resistor. At some point on this gradient the temperature reaches ade gree sufiicient to oxidize the carbon or graphite in contact with air which is most likely to leak into the furnace where the terminals pass through the furance wall. The burning of the terminals or resistor occurs where this critical temperature exists.

It has been common in electric furnaces to protect the resistor terminals from burning by constructing the terminals with a relatively large cross sectional area so that the current density is low. The terminals of an electric furnace pass through the furnace walls which make a heat insulating jacket around them and as there is necessarily considerable conduction of heat from the resistor, it is necessary to water cool the terminals throughout their entire lengths. The heat lost by conduction from the resistor to the terminals of relatively large cross sectional area is considerable and the terminals are apt to burn inside the furnace walls.

The object of this invention is to provide terminals for an electric furnace of rela tively small cross sectional area and to the place where the critical point in the temperature gradient occurs, and to make the gradient at that point as steep as possible which is most desirable at a point outside or as near as possible to the outside of the furnace because of the accessibility for repairs and replacements.

A further object of the invention is to provide a resistor terminal sealed into the furnace wall with a refractory material such as a silicon carbide mixture.

A further object of the invention is to provide a resistor terminal with an improved cooling means.

Serial No. 257,822.

Further objects and advantages of the invention will be apparent from the following specification and accompanying drawings, in Which- Fig. l is a horizontal sectional view of a portion of an electric furnace embodying the invention.

Fig. 2 is a vertical cross sectional view of Fig. 1.

Fig. 3 is a vertical cross sectional view of Fig. 2, and

Fig. 4 is a vertical cross sectional view of a part of an electric furnace showing a modification of the invention.

Referring to the drawings, the furnace F contains in its base in silicon carbide firesand in which the resistor 10 is embedded. The resistor 10 is supported by two inner carbonaceous terminal blocks 11 and 12 having threaded pins 13 and 14 which pass through apertures in the ends of the resistor and are held in assembled relation by carbonaceous terminal nuts 15 and 16, screwed onto the pins. This joint, although a good mechanical and electrical connection, is still a poor conductor of heat, serving to prevent considerable loss of heat from the resistor 10. The inner terminal blocks 11 and 12 are also drilled and threaded part way to receive the circular carbonaceous terminal rods 17 and 18. The opposite ends of the terminal rods are threaded into outer carbonaceous terminal blocks 19 and 20. The upper part of the outer terminal blocks 19 and 20 are recessed to receive a U bend of the continuous water circulating copper tubings 21 and 22 which extend through the outer walls of the furnace. The copper tubings are held rigidly in place with the terminal blocks 9 and 10 by means of soft metal inserts such as lead 28 and 24, which are introduced in a molten state. This joint be tween the copper tubes and the carbonaceous blocks is a good electrical connection, but a poor conductor of heat. Copper connectors 25 and 26 are attached to the outer ends of the copper tubing outside the furnace wall for the lead wire supplying the electric current to the furnace. The terminal rods and the outer blocks are covered with a protective coating 27 which is a refractory sub stance such as, for example, a silicon carbide mixture which becomes plastic when heated to a temperature below that at which the carbonaceous resistor burns. The cross sectional area of the terminal'rods l7 and 18 is such that when the furnace is in operation the protective coating 27 surrounding it becomes plastic.

ater is circulated through the copper tubings 21 and 22 when the furnace is in operation for keeping the tubes cool and the metal inserts 23 and 2a in a solid state.

There is an extremely steep temperature gradient between the ends of terminal rods 17 and 18 and the outer terminal blocks 19 and 20 due to the high thermal resistance of the contact between the rods and blocks and the cooling effect of the water flowing through the copper tubings 21 and 22 within the block. This temperature gradient is so steep in actual practice that the protective coating 27 becomes plastic not only over the end of the terminal rods 17 and 18 at the outer terminal blocks 19 and 20, but over the block itself. This plastic protective coating prevents oxidation of the carbonaceous material. Therefore, the only possible place where burning could occur, provided there is air leakage, is in the blocks 19 and 20 which from their position are easily accessible at all times and if destruction did occur could be readily replaced or repaired.

In Fig. at the outer terminal block 19 is shown as being located entirely outside of the furnace with the rod 17 extending through the wall. The resistor 10 in this structure is shown as a vertical resistor having threaded therein the inner end of the rod 17. This specific connecting means illustrated is not essential as the rod may be of any cross sectional shape such as rectangular or the like and attached to the outer end block 19 andresistor 10 by means of graphite bolts or cap screws or stud bolts.

It will be readily seen that by coating the carbonaceous terminal connections with a refractory protective mixture that is plastic but does not melt at a temperature slightly below that at which burning of the terminal takes place, by making the terminal rods of cross sectional areas that causes them to be raised throughout the greater part of their length to a temperature as high or higher than the temperature at which burning takes place and to provide a very steep temperature gradient along the terminal from the point at the temperature where burning takes place, a greatly improved terminal is obtained.

I claim:

1. An electric terminal for use in an electric resistor furnace comprising a resistor. a water cooled carbonaceous outer block and a carbonaceous rod of relatively small cross sectional area having a rigid connection to said resistor and to said outer block said connection between said rod and said outer block having a high thermal resistance.

2. An electric terminal for use in an elec tric resistor furnace comprising a carbonaceous means connected to the resistor of said furnace and a refractory coating for sealing said means within the walls of said furnace adapted to become plastic without melting at the temperature at which oxidation of said carbonaceous means begins to prevent oxidation of the carbonaceous means.

3. .An electric terminal for use in an electric furnace comprising an outer carbonaceous block an inner carbonaceous block and a carbonaceous rod connecting said blocks, a coating of refractory material surrounding said rod, said rod having a relatively small cross sectional area so that its temperature during operation of the furnace is sufficiently high to cause said refractory material to become plastic to prevent oxidation of said rod.

l. An electric terminal for use in an electric resistor furnace comprising a carbonaceous inner block rigidly attached to the resistor of said furnace, a carbonaceous outer block sealed into the wall of said furnace, a carbonaceous rod of relatively small 2.-

cross sectional area of high thermal resistance connecting said blocks and means for circulating water through said outer block and also forming a connecting means for the terminal to the source of electricity.

5. An electric terminal for use in an electric resistor furnace comprising a carbonaceous inner block attached to the resistor of said furnace, a recessed carbonaceous outer block sealed into the wall of said furnace, a carbonaceous rod of relatively small cross sectional area rigidly connecting said blocks and a U-shaped circulating tube sealed within the recess of said outer block for circulating water to cool said outer block and extending through the walls of said furnace to also form an electrical connection to the source of electricity.

6. An electric terminal for use in an electric resistor furnace comprising a carbonaceous rod, a carbonaceous block sealed within the walls of the furnace and secured to said rod and a refractory coating for said rod and block adapted to become plastic without melting at the temperature at which oxidation of said rod begins.

7. An electric terminal for use in an electric resistor furnace comprising a carbonaceous inner block secured to the resistor of the furnace, an outer water cooled carbonaceous block within the walls of said furnace. a carbonaceous rod of relatively small cross sectional area secured at each end to said blocks and a refractory coating for sealing said outer block and rod within the walls of said furnace adapted to become plastic without melting at the temperature at which oxidation of said rod begins.

8. An electric terminal for use in an electric resistor furnace comprising a carbonaceous inner block secured to the resistor of the furnace, an outer carbonaceous block within the walls of the furnace, a water cooling means extending through the walls of said furnace for cooling said outer block, a carbonaceous rod of relatively small cross sectional area secured at each end to said blocks and a refractory coating for sealing said outer block and rod within the walls of said furnace adapted to become plastic without melting at the temperature at which oxidation of said rod begins.

9. An electric terminal for use in an electric resistor furnace comprising a carbonaceous inner block secured to the resistor of the furnace, an outer recessed carbonaceous block within the Walls of the furnace, U- shaped water circulating tubing for cooling said outer block sealed within the recess of said outer block by a relatively soft metal and extending through the Walls of the furnace adapted to also form an electric connection with the source of electricity, a carbonaceous rod of relatively small cross sectional area secured at each end to said blocks and a refractory coating for sealing said outer block and rod within the walls of said furnace adapted to become plastic without meltin at the temperature at which oxidation 0 said rod begins.

10. An electric terminal for use in an electric furnace comprising an outer block within the Walls of the furnace, a rod of relatively small cross sectional area having a rigid connection with said block, means for cooling said block, said connection between said block and said rod having an extremely steep temperature gradient due to the high thermal resistance of the contact between said block and said rod of relatively small cross sectional area.

11. An electric terminal for use in an electric furnace comprising an outer block within the Walls of the furnace, a rod of relatively small cross sectional area having a connection with said block, means for cooling said block, said block and said rod being sealed within the walls of the furnace by a refractory coating material which becomes plastic without melting at the tempearture when oxidation of said rod begins, said connection between said block and said rod having an extremely steep temperature gradient due to the high thermal resistance of the contact between said block and said rod of relatively small cross sectional area.

JAMES KELLEHER. 

